The HPV vaccine can help prevent cervical cancer. Infections are to blame for 2 million instances of cancer worldwide, according to a new study. (Photo: REUTERS/Jessica Rinaldi)

Many people think of cancer as a result of genetics, but almost two million instances of cancer worldwide -- one in six -- are caused by treatable infections, according to a new study. Increasing vaccination efforts would go a long way to preventing many of these cases, researchers said in the study, published Wednesday in the Lancet Oncology.

Researchers looked at data on 27 cancers from 184 countries and found four infections responsible for many of the cancers caused by infection, all of which are preventable. The human papillomavirus causes cervical cancer, the bacterium Helicobacter pylori causes stomach cancer and hepatitis B and C can cause liver cancer, according to the study. Vaccines are available for all four.

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"Infections with certain viruses, bacteria, and parasites are one of the biggest and preventable causes of cancer worldwide," Catherine de Martel, study coauthor and researcher with the International Agency for Research on Cancer in France, said in a statement. "Application of existing public-health methods for infection prevention, such as vaccination, safer injection practice, or antimicrobial treatments, could have a substantial effect on future burden of cancer worldwide."

Some nastier infections, such as the Epstein-Barr virus and some types of herpes can cause cancer as well, but are much rarer.

The Centers for Disease Control and Prevention recommends the HPV vaccine or all girls and boys, but since the shot requires three doses spread out over the course of several months, few end up getting fully protected.

"Our vaccination program is gaining momentum but very slowly, and one reason is it's hard to get teenagers in for all three doses," William Schaffner, chairman of preventive medicine at Vanderbilt University Medical Center in Nashville, Tenn., told ABC News. "The other reason is that because HPV is sexually transmitted, it's evoked a whole bunch of hullaballoo over whether the vaccine promotes promiscuity. Of course, there's no evidence to support that at all."

He also said the hepatitis B vaccine will pay dividends in the future.

"We vaccinate all children against hepatitis B, so their risk of liver cancer down the road will be very much reduced," he said. "If we look back 20 years from now, we will see the occurrence of liver cancer dropping precipitously."

Researchers stressed that simply having one of these infections doesn't mean you'll get cancer -- it takes a while for it to occur.

"One thing that infection-associated cancers have in common is that a chronic infection is required," Martyn Plummer, study coauthor and researcher with the International Agency for Research on Cancer in France told Fox News. "It takes decades for an infection to progress to cancer."

Schaffner said there are many other causes of cancer, and people should take all precautions necessary to prevent the disease from occurring, which includes not smoking and eating a healthy diet.

"We have to remember that in our country behavioral risk factors still loom large," he told ABC News. "There are a number of strategies we can all employ to reduce our risk of cancer even more."